DESCRIPTION: Hereditary Non-Polyposis Colon Cancer (HNPCC) is the most common form of hereditary colon cancer. Recent studies indicate that most HNPCC is attributable to mutations in the mismatch repair genes hMSH2, hMLH1, PMS1 or PMS2. The availability of genetic testing for HNPCC affords an unprecedented opportunity for high risk family members to learn whether or not they carry a mutation in an HNPCC-associated gene, and consequently have an 80-90% risk of developing colon cancer. We propose to conduct a prospective controlled study to evaluate the psychological and behavioral impact of genetic testing for high risk members of HNPCC families. The Translocational Model of Stress and coping will be applied to explore the processes by which persons cope with genetic information and adopt recommended surveillance regimens. The specific aims are: 1) to evaluate the short and long-term impact of genetic testing for HNPCC-associated mutations; 2) to identify the appraisal and coping processes that enhance psychological well-being and adherence; and 3) to assess the moderating influence of coping style, perceived social support, and family environment on responses to genetic testing. Subjects will be a minimum of 520 male and female members of documented HNPCC families. Telephone interviews will be conducted prior to genetic testing to collect data on sociodemographics, risk factors and coping styles, and to establish baseline levels of psychological distress, functional health status, and adherence behavior. Data on social support and family environment will be collected via mailed questionnaires. The results of genetic testing (ie mutation carrier vs. noncarrier) will be presented at an individual genetic counseling session. All subjects will receive follow-up telephone interviews at 1, 6, and 12 months post disclosure. Persons who agree to participate in the study, but decline genetic testing, will receive the same telephone interviews. Multiple regression and structural equation modeling techniques will be used to evaluate the impact of genetic testing and test result, and to identify subject characteristics that influence key coping processes and outcomes.